Increased electrical nerve stimulation threshold of the sciatic nerve in patients with diabetic foot gangrene: a prospective parallel cohort study.

CONTEXT: Peripheral neuropathy may affect nerve conduction in patients with diabetes mellitus.

OBJECTIVE

This study was designed to test the hypothesis that the electrical stimulation threshold for a motor response of the sciatic nerve is increased in patients suffering from diabetic foot gangrene compared to non-diabetic patients.

DESIGN

Prospective non-randomised trial with two parallel groups.

SETTING

Two university-affiliated hospitals.

PARTICIPANTS

Patients scheduled for surgical treatment of diabetic foot gangrene (n = 30) and non-diabetic patients (n = 30) displaying no risk factors for neuropathy undergoing orthopaedic foot or ankle surgery.

MAIN OUTCOME MEASURE: The minimum current intensity required to elicit a typical motor response (dorsiflexion or eversion of the foot) at a pulse width of 0.1 ms and a stimulation frequency of 1 Hz when the needle tip was positioned under ultrasound control directly adjacent to the peroneal component of the sciatic nerve.

RESULTS

The non-diabetic patients were younger [64 (SD 12) vs. 74 (SD 7) years] and predominantly female (23 vs. 8). The geometric mean of the motor stimulation threshold was 0.26 [95% confidence interval (95% CI) 0.24 to 0.28] mA in non-diabetic and 1.9 (95% CI 1.6 to 2.2) mA in diabetic patients. The geometric mean of the electrical stimulation threshold was significantly (P < 0.001) increased by a factor of 7.2 (95% CI 6.1 to 8.4) in diabetic compared to non-diabetic patients.

CONCLUSION

The electrical stimulation threshold for a motor response of the sciatic nerve is increased by a factor of 7.2 in patients with diabetic foot gangrene, which might hamper nerve identification.